Exercise equipment designed to simulate climbing stairs or jogging has long been known. One known type of such exercise equipment includes a frame and two foot beams or pedals which are pivotally mounted to the frame. In this equipment, the pedals are depressed alternately as the user climbs or jogs in place. The pedals are returned to an upper, typically generally horizontal, position by one of a variety of biasing means.
One group of biasing means for returning the foot pedals to the upper position comprises a pair of coil springs, each of which are positioned beneath a respective one of the foot pedals, as disclosed in U.S. Pat. No. 3,628,791 and German Patent No. 2,243,794. The use of coil springs alone as a means for biasing the foot pedals on exercise apparatus to the upper position has been found to be undesirable because the resistance generated by the springs typically does not vary linearly with displacement of the foot pedals. Such nonlinear resistance makes it difficult to develop an even exercise cadence.
Another system for returning the foot pedals of a stair climbing exercise apparatus to the upper position is disclosed in U.S. Pat. No. 4,838,543 (the "'543 patent"). The '543 patent discloses a rope and pulley arrangement for returning the foot pedal from which the user has removed his or her weight to the upper position. The rope and pulley system comprises a pulley centrally located between and above the foot pedals and a rope trained about the pulley and attached to each of the foot pedals so that when one of the foot pedals is pressed down by the user, the rope attached thereto is pulled down which in turn causes the other end of the rope attached to the other foot pedal to be pulled up. As a result of this upward movement of the other end of the rope, the foot pedal attached thereto is moved to an upper position. Although the rope and pulley arrangement disclosed in the '543 patent functions satisfactorily, a desire exists to provide a mechanism for returning the unweighted pedal to the upper position which has a higher degree of reliability and durability than that of the rope and pulley arrangement disclosed in the '543 patent.
Torsion springs of the type comprising an elongate, metal coil spring fixed to a pivotally mounted member so that the longitudinal axis of the spring is parallel to or coaxial with the axis of rotation of the member have been used in exercise equipment for biasing various pivotally mounted lever mechanisms in a given direction and for opposing movement of such lever mechanisms in an opposite direction. For instance, U.S. Pat. No. 4,684,126 discloses a rowing exercise apparatus comprising a pair of arm levers, each having a torsion spring associated therewith for opposing movement of the arm levers in a first direction and for biasing the arm levers in an opposite direction. German Patent No. 2,145,884 discloses a foot exerciser for bedridden patients comprising two foot pedals which are pivotally mounted to a frame. The foot exerciser includes a torsion spring associated with each of the foot pedals for resisting movement of the pedals in a first direction and biasing the pedals in a second, opposite direction. Soviet Union Inventor's Certificate 618,118 discloses a gymnast's springboard comprising a pair of lever mechanisms and a pair of torsion springs associated with each of the lever mechanisms for urging the mechanisms in a first direction and opposing movement of the lever mechanisms in an opposite direction. The lever mechanisms engage a horizontal bed and urge the bed upwardly and oppose movement of the bed in a downward direction. In addition to being relatively costly, the use of elongate, metal coil springs as torsion springs in exercise apparatus for biasing lever mechanisms in a first direction tends to be undesirable due to inadequate longevity and durability of such torsion springs.
Thus, known mechanisms for returning the foot pedals of exercise apparatus to the upper position either do not function satisfactorily or lack sufficient durability and longevity.
Elastomeric torsion springs have been used in applications unrelated to exercise apparatus as a means for opposing rotation of various mechanisms in a first direction and for biasing the mechanism so as to cause it to rotate in a second, opposite direction. Such elastomeric torsion springs typically comprise an annular outer casing made from a rigid material such as steel or aluminum, an annular central member made from an elastomeric material and attached to the inside surface of the outer casing, and an inner casing which is also typically made from a rigid material such as steel or aluminum and is attached to the inner surface of the central member. In use, the inner casing is typically fixed to a first member and the outer casing is attached to a second member which is designed to pivot relative to the first member. As the second member is caused to rotate in a first direction relative to the first member, rotational force is applied to the central elastomeric member via the outer casing attached to the second member. Such rotation of the central member causes energy to be stored therein. When the second member is released the energy stored in the elastomeric central member is transmitted via the outer casing to the second member so as to cause the latter to rotate in an opposite direction relative to the first member. One such elastomeric torsion spring is distributed by B. F. Goodrich Company of Akron, Ohio, under the federally registered trademark TORSILASTIC.